Magnetically-triggered proximity switches, also known as limit switches, are commonly used for linear position sensing. Typically, magnetically-triggered proximity switches include a sensor that is adapted to detect the presence of a target without physically contacting the target. Typically, the sensor may include a switching circuit mechanism enclosed within a switch body of the proximity switch, and the switching circuit mechanism typically includes a lever and contacts that are biased into a first position that closes a normally closed circuit. When the target, which generally includes a permanent magnet contained within a housing, passes within a predetermined range of the sensor, the magnetic flux generated by the target magnet triggers the switching circuit mechanism, thereby displacing the switching circuit mechanism into a second position in which the normally-closed circuit is opened and a normally-open circuit is closed. The closing of the normally-open circuit is detected by a processor, and a signal is sent to an operator or an automated operation system to indicate the presence of the target within the predetermined range of the sensor. The target may be secured to a displaceable element of a system, such as a valve stem of a control valve, and the sensor maybe secured to a stationary element of the system, such as a control valve body. When so configured, the sensor can detect when the displaceable element has changed positions (such as when a closure member coupled to the valve stem of the control valve has displaced from an open position to a closed position) and send a signal to alert the operator or the automated operation system.
The switching circuit mechanism typically includes a conducting component that moves or pivots relative to a stationary conducting component to close the normally-open circuit. This relative motion requires that a conductor connecting the moving component to the non-moving component be flexible during operation, and this flexible component is typically a copper braided material (known as a “pigtail.”). Although effective in some applications, pigtails have several drawbacks. For example, pigtails are limited in size because the flexibility of the pigtail is a function of its length. That is, if the pigtail is too short, the pigtail will be too stiff to adequately flex during operation. Consequently, the pigtail may break or its stiffness may prevent the closing of the normally-open circuit. Also, because the pigtail is comprised of many thin conducting wires, the current the pigtail can conduct is limited. Consequently, there is a need for a switching circuit mechanism that overcomes the problems of the pigtail by eliminating the need for a continuously flexing conductor to connect the moving and non-moving components of the switching circuit mechanism while also not limiting the amount of current that is able to flow through the switching circuit mechanism.